Terephthalic acid is commercially produced by oxidation of paraxylene in the presence of a catalyst, such as, for example, Co, Mn, Br and a solvent. Terephthalic acid used in the production of polyester fibers, films, and resins must be further treated to remove impurities present due to the oxidation of para-xylene. Typical commercial process produce a crude terephthalic acid then dissolve the solid crude terephthalic acid in water at high temperatures and pressures, hydrogenating the resultant solution, cooling and crystallizing the terephthalic acid product out of solution, and separating the solid terephthalic product from the liquid as discussed in U.S. Pat. No. 3,584,039 herein incorporated by reference.
In many processes colored impurities from the benzil, and fluorenone families are hydrogenated to colorless products and leave the process with the terephthalic acid solid product and wastewater streams. However, this invention provides an attractive process to produce a purified carboxylic acid slurry by utilizing a solid liquid displacement zone comprising a solid liquid separator at elevated temperatures after oxidation of a crude carboxylic acid slurry product and prior to final filtration and drying.